The present invention relates to zoned heating and cooling systems and, in particular, to systems having a plurality of temperature sensors for separately regulating zone temperatures.
It is known to have a zoned heating or cooling system wherein a heating or cooling plant can operate either continuously or in response to demands from various zones. The continuous-operation system serves to distribute the output of a furnace or air conditioning unit to those zones requiring temperature adjustment. Such a system requires a plant with adjustable output levels. Most existing plants, especially in smaller installations such as homes, do not possess such an adjustable plant. The alternative method is a central plant which is started whenever one zone demands service. However, the central plant may be started for many consecutive short intervals, merely to service individual zones, which results in a highly inefficient firing sequence.
It is also known (U.S. Pat. No. 3,724,534) to employ a scanner that is coupled to a plurality of zone thermostats. Such a system can adjust the overall heating and cooling according to the sum of the zone requirements. However, while this method tends to respond to the cumulative needs of the entire system, it does not differentiate between the separate zones to direct more or less of the central plant's output to an individual zone requiring a large amount of service. Accordingly, such a system may result in an overshoot or undershoot of a zone's target temperature.
It is also known to employ a digital, programmable, wall thermostat for controlling heating and cooling systems. This system can include a digital processor with memory which responds to temperature sensors. While the system can schedule heating changes, it does not consider the specific requirements associated with zone heating or cooling.
Other known heating or cooling systems involve computer control, such that periods of time are divided into two intervals wherein the computer can consider a rapid heating or rapid cooling curve. These systems can consider outside weather conditions. However, such systems (U.S. Pat. No. 4,293,028) do not consider the specific requirements for regulating multiple zones in an efficient manner.
Also relevant are U.S. Pat. Nos. 4,200,910; 3,024,007; 4,215,408; 4,308,911 and 4,123,796.
Basic problems preventing the use of multiple zone heating/cooling in small environments, such as the home are: (1) the first cost, and (2) the great difficulty in regulating heating systems (forced air, for example), to provide efficient zoned heating. For example, a straightforward approach to achieve zoned heating with forced hot air is to provide separate room thermostats, so that the furnace is fired whenever a zone falls below a predetermined comfort level. The problem with this concept, as described above, is that the zones can demand heat randomly. It is, therefore, likely that the furnace will be cycling frequently to supply heat to the numerous unsynchronized zones. Starting the furnace for many brief intervals tends to be relatively inefficient because of a warm-up interval wherein energy is consumed in a furnace before useful heat is delivered from it.
Another advantage of using the foregoing is the possibility of preventing air conditioner evaporation coil icing which often occurs when airflow is restricted. Airflow is restricted when one or more zones are deactivated.